The Pros Appraise Excavator Design Concepts

Sept. 28, 2010

Local 150 operators Gene Held, in the foreground on the Bobcat 430 ZHS, and Tim Yednoch, on the Bobcat 331G, dig "footing corners" in super-stubborn material. Both X-change coupler system, which uses a spring loaded-wedge locking mechanism to facilitate attachment changes.
If you had to maneuver either the 331G or the 430 ZHS through restricted opening, the widest part of each machine would be the blade, which is essentially the same width as the undercarriage. Blade width is 60.6 inches for the 331G, and 70.1 inches for the 430 ZHS. In this aerial view, the upper structure of each machine has been rotated 90 degrees from its over the blade digging position.
If you had to maneuver either the 331G or the 430 ZHS through restricted opening, the widest part of each machine would be the blade, which is essentially the same width as the undercarriage. Blade width is 60.6 inches for the 331G, and 70.1 inches for the 430 ZHS.
Local 150's Tim Yednoch gives the engine bay of the 430 ZHS a close inspection. Access to routine service points, he says, should be no problem.
Comparing Lift Capacity

We were curious about how the lifting ability of the 331G and 430ZHS compare, so we added together the rated lift capacities for all of the “lift-radius/lift-point-height” combinations listed in each of the three sections of the 430’s load chart. We did the same for corresponding points on the 331’s load chart, then compared totals between the two machines. Here are the results of this unofficial comparison: Over the blade, with the blade down, the 430 has an advantage of 22 percent; over the blade with the blade up, the 331 has an 8 percent advantage; and over the side with the blade up, a 4 percent advantage goes again to the 331.

It's taken a while for the mini-excavator to catch on in North America. But today, these compact machines are working, unobtrusively, on small jobs and in small spaces just about everywhere. "Everywhere" now also includes the Apprenticeship and Skill Improvement facility that Local 150 (International Union of Operating Engineers) operates in Plainfield, Ill. Local 150 recently added two 3.5-metric-ton mini-excavators to its sizable fleet of earthmovers and cranes.

The Local's facility, of course, is the site of Construction Equipment's Hands-On-Earthmoving evaluations; and professional operators Tim Yednoch and Gene Held, instructors at the facility, are gracious enough to take a day out of their schedules now and then to run the subject machines and voice their opinions. As coincidence would have it, the machines that we most recently brought to them for evaluation were mini-excavators, a pair of Bobcat units, a 331G and the brand-new 430 ZHS (zero house swing) model.

Tim and Gene had not yet operated Local 150's smallest excavators, so running the Bobcat machines was a little something different in their day. Our purpose in bringing the Bobcat excavators to the experts was two-fold: To gauge how a couple of the best operators around would react to such small machines, and to get their opinions about the distinct design concepts reflected in the two machines.

The 331's design is that of a "conventional" mini, meaning that the rear portion of its rotating upper structure hangs over the tracks at any point in the swing circle. By comparison, the 430, with its "zero-house-swing" design, keeps the tail of its upper structure within the footprint of the tracks through the complete swing circle, and can keep its front corners tucked in for 320 degrees of the swing.

Tom Connor, Bobcat's excavator product specialist, suggested using the 331 and 430 for the evaluation, because their overall specs are close. Both have around 40 net horsepower, and both dig to a depth of slightly more than 10 feet. The 430 weighs more, however—8,024 pounds, versus the 331's 7,215 pounds—the result, primarily, of its enlarged undercarriage and its use of twin blade cylinders (the 331 uses just one).

The typical initial perception of the zero-house-swing design, says Connor, is that it compromises digging power, cab room and service access in the interest of keeping the upper structure tucked up within the undercarriage footprint for 90 percent of the swing circle. We were curious about what the Local 150 experts would think. On site to answer questions about machine design and application were Bobcat's Connor and Lance Mathern, marketing manager.

Room with a view...and more

Both machines on site were new units, supplied by the local Bobcat dealer (Atlas Bobcat), and both were equipped with enclosed cabs, heat and air conditioning. Since neither operator had yet had the chance to check out the machines, we asked them first to give both cabs the once-over. It's fair to say that both men were pleasantly surprised.

"For guys like Tim and me [both near 6 feet]," said Gene, "there's ample room. I found the cabs on both machines quite comfortable, and visibility is good all around."

Tim commented on the ease of entering the cab: "One step on the track, and another into the cab. It's an easy motion that won't wear you out if you're on and off the machine all day. And the cab door is wide enough that you don't have to turn sideways."

Not much about machine design escapes the attention of men who have spent 30-plus years on earthmovers. Tim noted that at the base of the right console on both machines was a lever that switched the joystick controllers between the "ISO" and "Standard" patterns.

"That's a nice feature," he said, "because you find operators who get familiar with one pattern, and find it difficult to adapt to the other. I actually prefer the ISO pattern, but you can learn to use either."

After an initial walk-around with the Bobcat representatives, the operators moved the machines to the worksite. Gene, on the 430, quickly left Tim, on the 331, as they say, in a cloud of dust. The reason, explained Connor, is that the 430 has two hydraulic pumps dedicated to the travel function. The 331's travel and work functions share a pump. Tim said he had dibs on the 430 on the return trip.

Machines at work

The work site was an area where equipment traffic had packed the soil (clay laced with rocks) really hard. We asked each operator to dig an L-shaped trench, about 2 feet deep and 8 feet long on the sides, similar to the corner of footing excavation. The operators then switched machines and duplicated the task. We then asked for their comments.

"They have a lot more power than I thought they'd have," said Gene. "The material we're digging in is really tough, and both machines got through it. I thought that stuff would pull them right down on their noses, but it didn't."

We were curious, of course, about how they compared the trenching ability of the zero-house-swing 430 to the conventional 331. (Boom and arm length are the same for the two machines, and buckets are identical.)

"Actually, I thought the 430 seemed to move through the material a bit stronger," said Tim. "It had more digging power or breakout power—whatever you want to call it."

Gene agreed that the 430 had the edge in digging power and, when we asked about stability, he said he would give an edge to the 430 on that count as well. Tim, though, said he did not really notice any difference in stability.

We then asked Gene and Tim to backfill the trenches with the machines' blades, again switching midway through the task. They agreed that the 331 and the 430 both had ample pushing power. Tim, however, initially found the 331 "a little jerky," by comparison with the 430, when maneuvering around the spoil pile.

"It's a matter of getting familiar with the machine," said Tim. "But for just jumping on the machines for the first time to backfill, the 430 maneuvers a lot smoother of the two."

Our final exercise was over-the-side digging. After both operators had dug for 15 minutes or so with each unit, we asked for their take on the machines' comparative stability. Tim found little difference between the two; Gene said that the 430 had just slightly more stability—"just a little more, in my opinion, maybe because of the wider tracks."

Then, with both units parked side-by-side, we asked the operators to assess whether the design of the engine and hydraulic compartments limited access to routine service points in either machine. Both agreed that access to the fundamentals—engine oil, hydraulic oil, engine coolant and filters (oil and fuel)—was not a problem for either machine.

Final considerations

After spending the day with the Bobcat machines, all of us had the same basic question for the Bobcat representatives. If the more-agile, zero-house-swing machine requires no apparent compromises in digging force, cab room or service access, then is this the direction Bobcat will take when redesigning models in the future?

"You have to keep in mind," said Connor, "that the 331 is 10 inches narrower than the 430, which might make it the preferred machine in some instances. If machine width is the primary concern, then the user may consider zero tail swing—or zero house swing—of little value."

Some users, he says, object to the zero-house-swing concept, because the machine gives the perception of being "too big" for a particular application.

"But it's my experience," says Connor, "that the perception often is incorrect, and that the machine would, in fact, fit the situation. Basically, the market will decide if the conventional mini will remain viable."